Mechanical studies for the rotational stability of a cemented stem in cases with stem anteversion adjustment in the cement mantle.

INTRODUCTION

The cemented stem can accommodate various shapes of femurs and is a stable stem with long-term results. Additionally, the cemented stem is a highly versatile stem that can be used to adjust stem anteversion in patients with variable femoral anteversion. On the other hand, rotating a stem with increasing cement viscosity may result in reduced postoperative rotational stability.

MATERIALS AND METHODS

Rotational stability was compared using two different cementing techniques via in vitro models. Six stems in Group S (Static) were inserted and fixed until the cement was completely hardened. Six stems in Group R (Rotation) were inserted and then rotated 15° before the cement had fully cured. After the cement had completely set, a static rotation testing was performed in which the stem was rotated at a rate of 1°/sec to 20° while a vertical load of 600 N was applied. For the dynamic testing, a vertical load of 600 N and 10,000 cycles of repetitive rotation were applied at 10° around the stem axis at 0.1 Hz. After 10,000 cycles, maximum torque was compared between Groups S and R.

RESULTS

In both groups, the torque value increased proportionally to the rotation angle. There were no significant differences in resistance to static rotation between Groups S and R (P = 0.599). In the dynamic testing, there was no significant difference between Groups S and R in both minimum torque and maximum torque in any of the cycles. There were no differences in the rotational torque between Groups S and R at 10,000 cycles (P = 0.693).

CONCLUSIONS

The rotational stability of the cemented stems did not decrease in vitro when stem version control was performed up to 15° before the cement had completely hardened.